Enthusiasts who take four-wheel drive vehicles off-road often modify their vehicles to enhance performance in such environments. Many modern four-wheel vehicles are equipped with non-serviceable unit-bearing hubs that combine a driving axle shaft, support bearings and a wheel hub. In such unit-bearing assembly designs, the axle shaft supports the front wheel. If the vehicle axle transmits power and supports the front wheel, the drive train is constantly rotating so drive line vibrations often occur. A common modification is a change in the suspension of the vehicle so that the body and chassis is raised up or “lifted” to provide more ground clearance. This results in even more driveline vibrations, particularly at highway speeds. Another common problem caused by “lifting” is that the steering geometries are changed and the vehicle can become unstable unless the steering knuckle provides a means to attach the steering components in a position that is similar to the factory attachment points.
In either a factory stock vehicle or a modified vehicle, there are numerous disadvantages to the unit bearing system. Since the axle shaft must both power and support the wheel, the shaft is highly loaded making it prone to failure. If the axle shaft fractures, there is nothing to hold the wheel in place and consequently, it can fall off the vehicle with predictably dangerous results. Another disadvantage with this system is that the drive train is constantly rotating which causes wear and tear on the drive train along with increased fuel consumption. If the vehicle suspension has been raised higher than delivered by the factory, the steering linkage and geometry is compromised, and the vehicle can become skittish when the vehicle hits bumps in the road.
A unit-bearing assembly is illustrated in FIG. 1, and includes a stub shaft 10 connected to an inside axle 11 by a universal joint 15. A steering knuckle 12 is mounted to an axle housing 13 at ball joints 14 and is linked to a vehicle steering assembly for steering. As shown, the unit bearing 16 is affixed to the steering knuckle 12, and a sleeve 17 on the wheel drive flange 18 is inserted in the unit bearing 16. An axle nut 19 is threaded on the stub shaft 10 at the wheel drive flange 18 securing the stub shaft 10 in position. The sleeve 17 on the wheel flange 18 has internal splines (not shown) that mate with external splines 20 on the stub shaft 10. Accordingly, as the inside axle 11 rotates the stub shaft 10 is rotated providing drive power to the wheel drive flange 18 on which a wheel (not shown) is mounted. Bearings 17 within the unit bearing 16 enable rotation of the wheel axle flange 18. Another disadvantage of these unit bearing systems is that if larger tires are mounted on wheel axle flange 18 the tires may be offset away from the vehicle to avoid the vehicle's chassis and inner fenders. This places an extreme amount of leverage on the axle or stub shaft 10, and the bearings 17 within the unit may not support the axle, which can break causing the wheel to fall off.
Some four-wheel drive models are equipped with spindle and wheel hub assemblies that include a spindle mounted to the steering knuckle wherein the stub shaft, having been connected to the inner front axle, passes through the spindle and into a wheel hub. A lock out hub is connected to the wheel hub and the end of the stub shaft at the wheel hub. A series of splines on the stub shaft end, the lock out hub and wheel hub enable the transfer of power from the stub shaft to the wheel hub. In this manner, the spindle supports the tire and wheel and allows an axle drive shaft to pass through the center of the spindle to provide power to drive the front wheels. Such a system provides a couple of advantages over the above-described unit bearing assemblies. One advantage is that if the front driving axle breaks the wheel remains supported by the wheel hub (and indirectly by the spindle) and does not fall off.
In addition, the lock out hub is operable to disconnect the stub shaft from the wheel hub allowing the wheel to rotate freely. This saves wear and tear on the drive train and improves gas mileage since the drive train is not spinning continuously. Also, using a spindle to support the wheel increases the strength of the front driving axle because the wheel support bearings are not loaded as highly.
Systems or kits are available to convert a unit-bearing front axle assembly to a spindle and wheel hub assembly. Dynatrac (www.dynatrac.com) located in Huntington Beach, Calif. provides such a kit, which is called a “stub-hub conversion” kit. This kit includes a stub shaft, spindle and wheel hub (among other components) that are custom designed to fit the existing unit-bearing steering knuckles or a Dynatrac steering knuckle, which is similar to the OEM unit bearing steering knuckles. However, existing OEM components and parts for spindle and wheel hub assemblies do not match either OEM or the Dynatrac unit bearing steering knuckles, because such components are designed for use with spindle design steering knuckles. Unfortunately, Dynatrac is the sole source of the spindle and wheel hub components that match and fit the unit-bearing steering knuckles. Accordingly, if parts to the Dynatrac kit are broken or otherwise rendered inoperable, the end user is limited to obtaining replacements from the single source and do not have the advantage of multiple sources. The Dynatrac spindle and wheel hub and related parts are not OEM parts. Accordingly, a need exists for a kit or steering knuckle to convert a unit bearing front axle that utilizes OEM spindle and wheel hub assembly components, and are not limited to custom spindle components.